Well in that case, it best that you learn 
an I mean every word, verb, noun, pronoun an then basically its just a case of going threw one by one.
An if its not that, then you need to learn all the welsh spellings of all the town, villages an cities.
As I said, I live in Swansea, but the welsh word for Swansea is Abertawe. So if its not a word then you could try all the names of the villages, towns an cities.
An even then if you still have no luck, then its a case of going threw one by one of Welsh names, both boys an girls.
So, if after trying all the words, verbs, nouns, pronouns of welsh and all the names of all the villages, towns an cities in Welsh, an all the names, both boys an girls, then I don't know what else you could try.
You could try castles names, obviously in Welsh an things like that, an maybe some names of train stations to, that are a bit different.
But if still no joy after all that, then let new know.
